Upon production of lithium ion secondary batteries, a base material is coated with an electrode material comprising an active substance such as a lithium compound, a binder such as polyvinylidene fluoride, and N-methyl-2-pyrrolidone (hereinafter referred to merely as “NMP”) as a solvent, and the resulting coated material is calcined to produce an electrode. The NMP generated in a gaseous state in the calcination step is recovered by an adsorption method or a water-absorbing method to thereby previously prepare an aqueous solution comprising the NMP at a concentration of not more than 80% in view of the problem of safety upon transportation. Thereafter, the thus prepared aqueous NMP solution is transported to chemical plants to purify the recovered NMP again into a high-purity NMP product. Meanwhile, in the chemical plants, the recovered NMP is purified by known distillation methods to obtain the purified NMP having a purity of not less than 99.9% which is similar to a purity of NMP initially produced.